Pulmonary inflammation and injury is a frequent (and, in some instances, lethal) outcome of virus infections of the respiratory tract. Respiratory virus infection triggers a coordinated response from the host innate and adaptive immune systems. The host response is essential for virus clearance and recovery, but is also a significant cause of pulmonary injury that can accompany virus elimination. Relevant recent examples of this are the immune-mediated lung inflammation/injury observed in human infections with the SARS coronavirus and the H5N1 avian influenza viruses. The long-term goal of Project 1 is to define and characterize the interactions between cells of the innate immune system i.e. dendritic cells, monocyte/ macrophage, NK cells and adaptive immune effector T lymphocytes (Tej in the process of virus clearance and in the control of inflammation/injury during experimental virus infection of the respiratory tract. The foundation for this application is our recent and unexpected findings in the murine model of type A influenza infection that anti-viral effector T-cells (both CD4 +Te and more prominently CDS +Te) infiltrating the infected lungs produce high levels of the anti-inflammatory/regulatory cytokines IL-10 during the Te response to infection and virus elimination. Furthermore, we found that blocking the effect of Te-derived IL- 10 during infection results in increased pulmonary inflammation and lethal injury. Our evidence further suggests that this Te-derived IL-10 plays a central role in controlling the level of lung inflammation/injury produced by mononuclear cells infiltrating the infected lungs in response to virus infection and the proinflammatory mediators released by virus- immune (Te). We wish to analyze the expression and regulation of IL-10 and specifically Te-derived IL-10 in the infected lungs and the impact of this cytokine on the control of virus clearance and lung inflammation/injury. The aims of Project 1 are: 1. To evaluate the cellular sources and effects of IL-10 on influenza virus infection; 2. To analyze the regulation of IL-10 production by Te during influenza infection; 3. To determine the impact of viral infection on the production of Te-derived IL- 10. The proposed studies are designed to complement ongoing related studies in Projects 2, 3 and 4.